<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>DOM</title>
</head>

<body>
    <div id="test" class="red">model</div>

    <div class="red">

        <div id="r1"></div>
        <div id="r2"></div>
        <div id="r3"></div>
    </div>

    <div id="travel">
        <div id="t1"></div>
        <div id="t2"></div>
        <div id="t3"></div>
    </div>
</body>
<script src="dom.js"></script>
<script src="main.js"></script>

</html>